In this field, prior art teaches the use of moulding machines for making parisons from thermoplastic material and machines for making the containers from the parisons by blow-moulding the parisons in moulds.
The parison moulding machine may be made according to different constructional types. For example, it may work according to a principle of injection, of injection and compression or of compression of the plastic material.
In the context of parison moulding machines, the term PAM (Preform Advanced Moulding) is also used to denote a system for producing parisons, or preforms, of PET by compression moulding technology.
Moulding machines of this kind are in any case usually rotary machines which make and feed out parisons in continuous cycle.
Usually, the parisons feeding out of the moulding machine are warm as a result of the heat produced during the moulding process just completed.
As to the blow-moulding machine, that is to say, the machine which makes the containers from the parisons by blowing the parisons in moulds, it should be noted that it too is a rotary machine.
In the blow-moulding machine, the parisons are first placed inside blow-moulds, individually or in groups and a fluid under pressure is then blown into each parison in such a way that the parison expands and takes on the shape of the cavity defined by the mould in which it has been placed.
In order to mould the parisons by blowing in this way, the parisons must, when they are fed into the blow-moulding machine, be at a temperature such that the part of each parison to be expanded is just viscous enough to allow it to expand without being damaged.
For this purpose, an oven connected to the outfeed side of the moulding machine and to the infeed side of the blow-moulding machine is used.
The oven is designed to receive the parisons (which are not at the right temperature for blow-moulding) and to heat them so that they can be fed to the blow-moulding machine under optimum temperature conditions for blow-moulding.
In light of this, it should be noted that the parisons have a body with a closed bottom and a neck which defines an opening.
During blow-moulding, the body of the parison must expand, while the neck must remain the same in shape.
Thus, for blow-moulding, the body of the parison must be hot and the neck must be cold (that is, at ambient temperature).
In light of this, it is known (for example from patent document WO03024693A1) that the oven comprises heating means operating in particular on the bodies of the parisons.
Thus, known in the prior art (for example from patent document WO2009/127962 in the name of the same applicant as this invention) is a plant for making containers of thermoplastic material in continuous cycle comprising: a rotary moulding machine for making parisons; an oven for heating the parisons, connected to the moulding machine and equipped with heating means operating on the bodies of the parisons; and a rotary blow-moulding machine configured to receive the parisons heated in the oven and to blow-mould them in moulds to make the containers.
In a plant of this kind, which comprises a combination of a parison moulding machine and a blow-moulding machine, both working in continuous cycle, the problem arises of how to deal with situations where one of the two machines needs to be shut down for a certain length of time, while the other machine is potentially able to continue working.
In view of this, the goal to be achieved is that of maximizing the productivity and efficiency of the plant under all circumstances.
More specifically, the problem to be solved is how to best deal with the situation where the blow-moulding machine stops (due to a breakdown or for any other reason), while the parison moulding machine is in a condition to continue working correctly.
This problem is tackled by patent document WO2009/127962.
Indeed, the plant described in patent WO2009/127962 comprises a transfer carousel, interposed between the blow-moulding machine and the oven and configured to define variable lengths time the parisons, or preforms, remain in the transfer carousel.
This allows the parisons feeding out of the moulding machine to cool down and then, if necessary, stored in a buffer (that is, a storage system or device, accumulation means, or a warehouse). The buffer or warehouse is preferably automatic.
This solution is not, however, free of disadvantages.
One disadvantage is due to the constructional complexity, and hence the cost of the plant, on account of a transfer carousel of this kind.
Another disadvantage is due to the overall dimensions of the plant, again due to the presence of the transfer carousel.